1. Field of the Invention
Further, the invention relates generally to electronic materials processing, and more particularly to a system and method for performing a patterning process without using photolithography.
2. Related Art
Modern video and computer LCD (liquid crystal display) displays typically include large arrays of thin film transistors (TFTs) for addressing the individual pixels in the displays. As the demand for larger LCD displays continues to rise, the TFT arrays used in those LCD displays must include increasing numbers of TFTs and more complex interconnect structures. In addition, the need for large display areas complicates the fabrication of these devices using conventional semiconductor processes. In combination, these factors result in ever-increasing TFT array size and complexity.
To reduce some of the costs associated with the production of these larger LCD displays, a liftoff process is sometimes used to generate the patterned layers that make up the TFT array. In a conventional liftoff process, a base layer on which a patterned photoresist layer is formed is blanket-coated with an overlying thin film, typically a metal layer. Then, the patterned photoresist layer is stripped, which removes those portions of the metal layer formed on top of the patterned photoresist layer, leaving a patterned metal layer on the base layer. This process is illustrated in FIGS. 1A-1F.
FIG. 1A shows a substrate 110 on which a photoresist layer 120 has been formed. In FIG. 1B, a lithography operation using a photomask 130 to expose a portion 121 of photoresist layer 120. Then, in FIG. 1C, a surface treatment operation is performed on photoresist layer 120 to create a surface 121 that develops more slowly than the underlying portion of photoresist layer 120. Note that this surface treatment may alternatively be performed before the exposure step shown in FIG. 1B.
In FIG. 1D, the unexposed portions of photoresist layer 120 are stripped from substrate 110, leaving a photoresist feature 121A (corresponding to portion 121 in FIG. 1B). Because treated surface 122 shown in FIG. 1C develops at a slower rate than the underlying portions of photoresist layer 120, the top of developed photoresist feature 121A overhangs the sidewalls of photoresist feature 121A, thereby creating the undercut profile shown in FIG. 1D.
Next, in FIG. 1E, a metal layer 130 is blanket deposited over substrate 110 and photoresist feature 121A. A photoresist strip operation is then performed to dissolve patterned photoresist feature 121A. The overhang region of patterned photoresist feature 121A results in thinned or even uncoated attack points 131 and 132 that allow the photoresist stripper to reach patterned photoresist feature 121A (in the case of the thinned attack points 131 and 132, the photoresist stripper can penetrate metal layer 130 through naturally occurring pinholes). When patterned photoresist feature 121A is stripped, the portion of metal layer 130 formed over resist feature 121A is lifted off substrate 110, resulting in a patterned metal layer 130A, as shown in FIG. 1F.
By eliminating the need for a separate etch process to create patterned metal layer 130A (in FIG. 1F), the conventional (photoresist-based) liftoff process described with respect to FIGS. 1A-1F can simplify the overall production process, thereby reducing production costs. However, patterning photoresist layer 120 (in FIG. 1B) still requires a photolithography process. For cost-reduction purposes, it is generally desirable to minimize the number of photolithography process steps required. This is not only due to the demanding nature of the photolithography process itself, but also due to the time and costs involved in producing the delicate photomasks used in the photolithography process.
Accordingly, it is desirable to provide a system and method for performing a liftoff process that does not require photolithography.